It contains no nerves or blood vessels, and its structure is relatively simple. If a thin slice of cartilage is examined under the microscope, it will be found to consist of cells of a rounded or bluntly angular form, lying in groups of two or more in a granular or almost homogeneous matrix.
These cells have generally straight outlines where they are in contact with each other, with the rest of their circumference rounded. They consist of translucent protoplasm in which fine interlacing filaments and minute granules are sometimes present. Embedded in this are one or two round nuclei with the usual intranuclear network. Fibrous cartilage has lots of collagen fibers Type I and Type II , and it tends to grade into dense tendon and ligament tissue. White fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions.
It owes its flexibility and toughness to the fibrous tissue, and its elasticity to the cartilaginous tissue. It is the only type of cartilage that contains type I collagen in addition to the normal type II. Fibrocartilage is found in the pubic symphysis, the annulus fibrosus of intervertebral discs, menisci, and the temporal mandibular joint. Elastic or yellow cartilage contains elastic fiber networks and collagen fibers. The principal protein is elastin. Elastic cartilage is histologically similar to hyaline cartilage but contains many yellow elastic fibers lying in a solid matrix.
These fibers form bundles that appear dark under a microscope. They give elastic cartilage great flexibility so it can withstand repeated bending.
Chondrocytes lie between the fibers. Elastic cartilage is found in the epiglottis part of the larynx and the pinnae the external ear flaps of many mammals, including humans.
Chondrification also known as chondrogenesis is the process by which cartilage is formed from condensed mesenchyme tissue. A chondrocyte: A chondrocyte, stained for calcium, showing its nucleus N and mitochondria M. Mesenchyme tissue differentiates into chondroblasts and begins secreting the molecules that form the extracellular matrix ECM. Mesenchymal stem cells MSCs are undifferentiated, meaning they can give rise to different cell types.
When the excitational radio frequency is peaked on a specific sodium species 23 Na , the relative fixed charge density of cartilage may be quantified, which is a function of the spatial resolution of charged proteoglycans. The imaging of articular cartilage remains challenging owing to the zonal changes in structure and biochemical composition over a few millimeters.
The potential for artifacts associated with MRI adds another dimension of complexity to this imaging dilemma. Articular cartilage is a highly specialized connective tissue of diarthrodial joints. Its principal function is to provide a smooth, lubricated surface for articulation and to facilitate the transmission of loads with a low frictional coefficient. The mechanical behavior of this tissue depends on the interaction of its fluid and solid components.
The unique and complex structure of articular cartilage continues to make its treatment and repair a significant challenge. No potential conflict of interest declared. National Center for Biotechnology Information , U. Journal List Sports Health v. Sports Health. Alice J. Sophia Fox. Scott A. Author information Article notes Copyright and License information Disclaimer. Keywords: articular cartilage, basic science, extracellular matrix, collagen, proteoglycan, chondrocyte.
This article has been cited by other articles in PMC. Open in a separate window. Figure 1. Gross photograph of healthy articular cartilage in an adult human knee. Structure and Composition of Articular Cartilage Articular cartilage is hyaline cartilage and is 2 to 4 mm thick.
Figure 2. Regions In addition to zonal variations in structure and composition, the matrix consists of several distinct regions based on proximity to the chondrocytes, composition, and collagen fibril diameter and organization. Chondrocytes The chondrocyte is the resident cell type in articular cartilage. Proteoglycans Proteoglycans are heavily glycosolated protein monomers. Figure 3. Noncollagenous Proteins and Glycoproteins Although a number of noncollagenous proteins and glycoproteins are found within articular cartilage, their specific function has not been fully characterized.
Metabolism In adults, the articular cartilage matrix is separated from the subchondral vascular spaces by the subchondral plate. Biomechanical Function Articular cartilage is a thin layer of specialized connective tissue with unique viscoelastic properties. Figure 4. Figure 5. Age and Development Age determines the composition of the ECM as well as the organization of chondrocytes and their response to external factors such as cytokines.
Mri In Articular Cartilage Noninvasive imaging techniques are an important tool for the evaluation, diagnosis, and monitoring of articular cartilage. Summary Articular cartilage is a highly specialized connective tissue of diarthrodial joints. Footnotes No potential conflict of interest declared. References 1.
Tensile properties of human knee joint cartilage: I. Influence of ionic cartilage conditions, weight bearing and fibrillation on the tensile modulus.
J Orthop Res. Cartilage restoration, part I: basic science, historical perspective, patient evaluation and treatment options. Am J Sports Med. Finite deformation biphasic material properties of bovine articular cartilage from confined compression experiments. J Biomech. Gd-DPTA2- as a measure of cartilage degradation. Magn Reson Med. Nondestructive imaging of human cartilage glycosaminoglycan concentration by MRI. Buckwalter JA. Articular cartilage: injuries and potential for healing.
J Orthop Sports Phys Ther. Articular cartilage: composition and structure. Injury and Repair of the Musculoskeletal Soft Tissues. Articular cartilage, part 1: tissue design and chondrocyte-matrix interaction. J Bone Joint Surg Am. Articular cartilage: tissue design and chondrocytes-matrix interactions.
Instr Course Lect. Restoration of injured or degenerated articular cartilage. J Am Acad Orthop Surg. Technology insight: adult stem cells in cartilage regeneration and tissue engineering. Nat Clin Pract Rheumatol. Cartilage imaging techniques: current clinical applications and state of the art imaging. Clin Orthop Relat Res. Matrix compartments in the growth place of the proximal tibia of rats.
Anat Rec. Articular cartilage collagen: an irreplaceable framework? Eur Cell Mater. Cartilage electromechanics: I.
Electrokinetic transduction and the effects of electrolyte pH and ionic strength. Future of MR imaging of articular cartilage. Semin Musculoskeletal Radiol. Guilak F, Mow VC.
The mechanical environment of the chondrocyte: a biphasic finite element model of cell—matrix interactions in articular cartilage. Hardingham T, Bayliss M. Proteoglycans of articular cartilage: changes in aging and in joint disease. Semin Arthritis Rheum.
Flow-independent viscoelastic properties of articular cartilage matrix. Elastic cartilage is histologically similar to hyaline cartilage but contains many yellow elastic fibers lying in a solid matrix.
These fibers form bundles that appear dark under a microscope. They give elastic cartilage great flexibility so it can withstand repeated bending. Chondrocytes lie between the fibers. Elastic cartilage is found in the epiglottis part of the larynx and the pinnae the external ear flaps of many mammals, including humans.
Key Takeaways. Key Points Cartilage is a flexible connective tissue that differs from bone in several ways; it is avascular and its microarchitecture is less organized than bone. Cartilage is not innervated and therefore relies on diffusion to obtain nutrients.
This causes it to heal very slowly. The main cell types in cartilage are chondrocytes, the ground substance is chondroitin sulfate, and the fibrous sheath is called perichondrium. There are three types of cartilage: hyaline, fibrous, and elastic cartilage.
Hyaline cartilage is the most widespread type and resembles glass. In the embryo, bone begins as hyaline cartilage and later ossifies. They rarely form cell-cell contact and are simply responsible for maintaining their immediate surroundings. Figure 3 shows the basic structure of a chondrocyte. The hyaline cartilage is generally covered by the perichondrium. The perichondrium is found in developing bones but does not cover the articular cartilage on the ends of bones in adults. The perichondrium consists of an outer layer and an inner layer.
The outer layer is fibrous cartilage and produces collagen fibers and the inner layer is involved in the formation of cartilage by forming chondroblasts or chondrocytes.
Articular cartilage is a type of hyaline cartilage. It is different from usual hyaline cartilage as it has flattened chondrocytes near the surface. In humans, it is 2 to 4 mm thick.
It does not have blood vessels, nerves, or lymphatics. Its ECM is dense whereas chondrocytes are sparse. Deeper in the tissue, the chondrocytes take a more typical structure. In the very deep layers of the cartilage, the cells are found in columns with a calcified matrix. The collagen fibers form arches giving it a strong structural arrangement to withstand pressure.
Figure 4 shows the location of the articular hyaline cartilage in a joint. Articular cartilage is made up of different zones. These include the superficial zone, followed by the middle transitional zone, the deep zone, and finally the calcified zone. Within each zone, there are 3 regions. These are the pericellular region, the territorial region, and the interterritorial region.
The video below presents the layers found in articular cartilage. Collagen fibers II and IX can be found here. It contains a large volume of chondrocytes that have a more flattened appearance. The superficial zone is in direct contact with the synovial fluid and protects the deeper layers from force and stresses. The middle zone follows directly from the superficial zone and provides the bridge to the deeper layers. It consists of thicker collagen fibers and proteoglycans. The chondrocytes here are spherical and found in small amounts.
The middles zone functions to protect against compacting forces. The deep zone follows on from the middles zone and provides the best resistance to compacting forces. It contains the highest proteoglycan content and the least water content. The collagen fibers are arranged at right angles to the surface and the chondrocytes are arranged in columns. Finally, the calcified zone attaches the cartilage to the bone. It does this by anchoring the collagen fibers in the deep zone to the subchondral bone.
As mentioned above, hyaline cartilage connective tissue is made up of cells and fibers within an extracellular matrix. Hyaline cartilage histology describes how hyaline cartilage looks when viewed under a microscope.
The chondrocytes can be seen as rounded or angular in form. In adult cartilage, the cells are present in isogenous groups, formed from a single progenitor cell. The matrix is visually homogenous and basophilic in appearance. The reason for this is because of the high concentration of sulfated GAGs in the matrix mask the collagen fibers. Type II collagen fibers are also very small which is why the extracellular matrix appears so shiny and smooth. There is no uniform distribution within the extracellular matrix.
Therefore, the three basic zones can be seen. Figure 5. Shows these different zones. The Van Geison stain uses picric acid and acid fuchsin and stains collagen red. The cartilage is viewed as a red zone lying below the epithelium.
The staining is lighter where it becomes closer to the lacunae indicating the territorial matrix. The territorial matrix is dark, and the interterritorial matrix is a lot lighter in color. These chondrocytes are derived from the same progenitor and are therefore an isogenous group. The perichondrium surrounds the cartilage except in the articular cartilage. There are 3 different cartilage types found in the body. Hyaline cartilage is the most common but also the weakest type of cartilage.
0コメント